The visual pigments of man are formed by the interaction of a polyene chromophore, ll-cis-retinal 1 or ll-cis-3-dehydroretinal 2 as their chromophore. The absorption and activation spectra of visual pigments show a wide range of lambda max values, and abnormal human vision has been correlated with abnormalities or absence of retinal visual pigments. Visual pigments formed with but a single chromophore (e.g. ll-cis-retinal 1) may vary greatly in spectral sensitivity, and it is generally accepted that the opsin determines the lambda max of the visual pigment. It appears that the fine structure of the opsin chromophore binding site defines the spectral characteristics of the visual pigment. This infers that different visual pigment opsins vary in primary structure. We propose to define and compare the primary structure of visual pigment proteins from different species, which display the same of different lambda max, in order that regions of sequence conservation and sequence variation may be identified which are of importance for visual pigment spectral sensitivity or visual pigment physiology. Initial comparative studies will concentrate on the amino acid sequences adjacent to functionally active groups (e.g. the photo-exposed sulfhydryl group).